To test the hypothesis that alcohol impairs error detection (Ridderinkhof et al., 2002), we calculated the proportion of both correct-response and error trials on which participants correctly judged the accuracy of their responses and tested whether these proportions differed across beverage groups using one-way ANOVAs. Accuracy judgment data from two participants (1 alcohol, 1 placebo) were not recorded because of software problems, leaving the sample size for these analyses at 65. For ease of interpretation, only trials for which participants made “sure correct” and “sure incorrect” judgments were included. Inspection of the means in Figure 7 (right-hand side) suggests that participants in the alcohol group were no less aware of their errors than participants in the other groups. Indeed, a significant effect of Beverage, F(2, 62) = 3.51, p < .05, indicated that participants in the alcohol group were more accurate (M = .87) than control group participants (M = .72), t(43) = 2.65, p < .05, and just as accurate as placebo group participants (M = .81), t(43) = 1.34, p = .19, at detecting when they had responded
